1. Field of the Invention
Embodiments described herein generally relate to a magnetic head and magnetic disk drive for use in a hard disk drive (HDD). More specifically, embodiments described herein relate to a magnetic head and magnetic disk drive used in shingled magnetic recording (SMR).
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
As the areal storage density in HDDs increases, the demand for a larger magnetoresistive effect has led to extensive research efforts worldwide. In a conventional perpendicular magnetic recording (PMR) method where track widths have become narrower as a result of size reduction of recording heads, it is difficult to achieve both further size reduction for recording heads and improvement in the magnetic field strength generated. As a result, although various improvements have been made, it is generally considered that a recording density of about 1 Tbpsi (Tera bit per square inch) is a limit of areal storage density in the conventional PMR.
A recording system for achieving a recording density in excess of 1 Tbpsi is SMR. In SMR, a part of a track is recorded overlapped in the track width direction and the remaining portion is used as a data track. Because one side of the trace is written overlapped, it is possible to use recording heads with a wide magnetic pole. Therefore, the track pitch can be narrowed while maintaining a large magnetic field strength. The read head used in the SMR method may be the same as the read head used in the PMR method. For example, a read head using a spin valve device may be used. Hard disk type read heads with a hard magnetic body disposed in the track width direction of the spin valve and side shield type read heads generally attempt to reduce the spread in the read sensitivity distribution in the track width direction by using a soft magnetic body instead of a hard magnetic body. In general, these read heads are designed so that their read sensitivity distribution becomes symmetric in the off-track direction.
Signal distribution and noise distribution of data tracks recorded with the SMR method may not necessarily be symmetric left to right as a result of different ways used to form the edges at the two sides of the data track. For example, the edge of the data track on one side is formed by overwriting and the edge on the other side is formed by being overwritten. When a read head with left to right symmetry in the off-track direction is used, a high signal to noise ratio (SNR) cannot be obtained in the SMR method. Achieving a high SNR generally allows for higher areal density recording.
Therefore, there is a need in the art for a read head which is capable of obtaining a high SNR in the SMR method.